This disclosure relates to a fuel vapor recovery apparatus including an adsorbent canister capable of capturing fuel vapor, a vapor passage introducing the fuel vapor produced in a fuel tank to the adsorbent canister, an atmospheric air passage fluidly communicating the adsorbent canister with the atmosphere, and a purge passage introducing the fuel vapor captured in the adsorbent canister to an intake pipe of an internal combustion engine.
Japanese Laid-Open Patent Publication No. 2007-177728 discloses a conventional fuel vapor recovery apparatus. Referring to FIG. 18, such conventional fuel vapor recovery apparatus 100 has an adsorbent canister 102 capable of trapping fuel vapor, a vapor passage 104 introducing the fuel vapor produced in a fuel tank 103 to the adsorbent canister 102, an atmospheric air passage 105 fluidly communicating the adsorbent canister 102 with the atmosphere, and a purge passage 107 introducing the fuel vapor captured in the adsorbent canister 102 to an intake pipe 120 of an internal combustion engine (not shown). The purge passage 107 is provided with a purge pump 110 for generating gas flow from the adsorbent canister 102 through the purge passage 107 to the intake pipe 120 of the engine. The purge passage 107 is further provided with a flow control valve 112 downstream of the purge pump 110. According to the above-described configuration, when the purge pump 110 is started under a condition where the engine is running, the atmospheric air is drawn into the adsorbent canister 102 through the atmospheric air passage 105 in order to forcibly purge the fuel vapor captured in the adsorbent canister 102 and introduce the fuel vapor into the intake pipe 120 of the engine. During this operation, the flow control valve 112 can regulate a flow rate of the gas flowing through the purge passage 107 toward the intake pipe 120 of the engine.
The fuel vapor recovery apparatus 100 is configured such that when the purge pump 110 provided along the purge passage 107 is driven, the fuel vapor adsorbed in the adsorbent canister 102 is forcibly purged by the air. Thus, there is a possibility that inner pressure of the purge passage 107 upstream of the flow control valve 112 becomes higher than the atmospheric pressure. When the engine is stopped under a condition where the inner pressure of the purge passage 107 is higher than the atmospheric pressure, inner pressure of the adsorbent canister 102 fluidly communicating the purge passage 107 becomes higher than the atmospheric pressure after the purge pump 110 is stopped. Accordingly, there is a possibility that the fuel vapor adsorbed in the adsorbent canister 102 diffuses to the atmosphere through the atmospheric air passage 105 due to the positive pressure in the adsorbent canister 102. Therefore, there has been a need for an improved fuel vapor recovery apparatus.